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DMA Timers (DTIM0–DTIM3)
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
22-8 Freescale Semiconductor
22.3 Functional Description
22.3.1 Prescaler
The prescaler clock input is selected from the internal bus clock (f
sys
divided by 1 or 16) or from the
corresponding timer input, DTINn. DTINn is synchronized to the internal bus clock, and the
synchronization delay is between two and three internal bus clocks. The corresponding DTMRn[CLK]
selects the clock input source. A programmable prescaler divides the clock input by values from 1 to 256.
The prescaler output is an input to the 32-bit counter, DTCNn.
22.3.2 Capture Mode
Each DMA timer has a 32-bit timer capture register (DTCRn) that latches the counter value when the
corresponding input capture edge detector senses a defined DTINn transition. The capture edge bits
(DTMRn[CE]) select the type of transition that triggers the capture and sets the timer event register capture
event bit, DTERn[CAP]. If DTERn[CAP] and DTXMRn[DMAEN] are set, a DMA request is asserted. If
DTERn[CAP] is set and DTXMRn[DMAEN] is cleared, an interrupt is asserted.
22.3.3 Reference Compare
Each DMA timer can be configured to count up to a reference value, at which point DTERn[REF] is set.
If DTMRn[ORRI] is set and DTXMRn[DMAEN] is cleared, an interrupt is asserted. If DTMRn[ORRI]
and DTXMRn[DMAEN] are set, a DMA request is asserted. If the free run/restart bit DTMRn[FRR] is
set, a new count starts. If it is clear, the timer keeps running.
22.3.4 Output Mode
When a timer reaches the reference value selected by DTRR, it can send an output signal on DTOUTn.
DTOUTn can be an active-low pulse or a toggle of the current output, as selected by the DTMRn[OM] bit.
IPSBAR
Offset:
0x00_040C (DTCN0)
0x00_044C (DTCN1)
0x00_048C (DTCN2)
0x00_04CC (DTCN3)
Access: User read/write
313029282726252423222120191817161514131211109876543210
R
CNT (32-bit timer counter value count)
W
Reset00000000000000000000000000000000
Figure 22-7. DMA Timer Counters (DTCNn)
Table 22-7. DTCNn Field Descriptions
Field Description
31–0
CNT
Timer counter. Can be read at anytime without affecting counting. Any write to this field clears it.